Method of selectively shaping hollow fibers of heat exchange catheter

ABSTRACT

A group of multiple hollow fibers may be shaped to introduce angular divergence among the fibers, or to introduce a selected longitudinal oscillation into the fibers. In one shaping technique, the fibers are held in parallel while upper and lower crimping assemblies of parallel crimping bars are drawn together on opposite sides of the parallel fibers. When bars of the opposing assemblies draw sufficiently close, they sandwich the fibers in between them, causing each fiber to assume a shape that oscillates as the fiber repeatedly goes over and then under successive bars. Since the crimping bars are aligned at oblique angles to the fibers, the peaks and troughs of successive fibers are offset. While in this position, the fibers are heated and then cooled to permanently retain their shapes. A different shaping technique utilizes a lattice of criss-crossing tines defining multiple apertures. In this technique, the lattice and fibers are positioned so that each fiber passes through one of the apertures. Then, the lattice and/or the fibers are slid apart or together until the lattice holds the fibers in a desired configuration, where the fibers have a prescribed outward divergence relative to each other. While in this position, the fibers are heated and then cooled to permanently retain this angular divergence. The heating can be effected using heating fluid or gas circulated in the bars.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/321,515 filed May 27, 1999, now U.S. Pat. No. 6,165,207.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to catheters that utilize a bundle of manysmall fibers to conduct heat or materials exchange with a target area ofthe human body. More particularly, the invention concerns a cathetermanufacturing process that selectively shapes a group of multiple hollowfibers to introduce angular divergence among the fibers or to introducea selected longitudinal oscillation into the fibers.

2. Description of the Related Art

In warm blooded creatures, temperature regulation is one of the mostimportant functions of the body. Despite the known importance ofproperly maintaining body temperature, scientists have discoveredcertain beneficial effects of artificially inducing a hypothermic state.For instance, cooling the body can help regulate vital functions duringsurgery by lowering the metabolism. With stroke, trauma, and otherpathological conditions, hypothermia is believed to also reduce thepermeability of the blood/brain barrier. Induced hypothermia is believedto additionally inhibit the release of damaging neurotransmitters,inhibit calcium mediated effects, inhibit brain edema, and lower intracranial pressure. Regardless of the particular mechanism, the presentinvention understands that fevers degrade the outcomes for patientssuffering from brain trauma or stroke, and moreover that hypothermia canimprove the outcomes for such patients.

Hypothermia may be induced locally or systemically. With localhypothermia, physicians focus their cooling efforts on a particularorgan, limb, anatomical system, or other region of the body. Withsystemic hypothermia, doctors universally lower body temperature withoutparticular attention to any body part.

Under one technique for inducing systemic hypothermia, physicians coolthe patient's entire body by packing it in ice. Although this techniquehas been used with some success, some physicians may find it cumbersomeand particularly time consuming. Also, it is difficult to preciselycontrol body temperature with ice packing. As a result, the patient'sbody temperature overshoots and undershoots the optimal temperature,requiring physicians to add or remove ice. Furthermore, there is somedanger of injuring the skin, which is necessarily cooled more than anyother body part.

In another approach to systemic hypothermia, the patient is covered witha cooling blanket, such as an inflatable air- or water-filled cushion.Beneficially, cooling blankets offer improved temperature controlbecause physicians can precisely regulate the temperature of theinflation medium. Nonetheless, some delay is still inherent, first for acooling element to change the temperature of the cooling medium, andthen for the temperature adjusted cooling medium to cool the desiredbody part. This delay is even longer if the targeted body part is aninternal organ, since the most effective cooling is only applied to theskin, and takes some time to successively cool deeper and deeper layerswithin the body.

The present invention recognizes that a better approach to inducinghypothermia is by circulating a cooling fluid through a cooling catheterplaced inside a patient's body. The catheter may be inserted into veins,arteries, cavities, or other internal regions of the body. The presentassignee has pioneered a number of different cooling catheters andtechniques in this area. Several different examples are shown U.S.application No. 09/133,813, entitled “Indwelling Heat Exchange Catheterand Method of Using Same,” filed on Aug. 13, 1998. Furthe, examples areillustrated in U.S. application No. 09/294,080, entitled “Catheter WithMultiple Heating/Cooling Fibers Employing Fiber Spreading Features,”filed on Apr. 19, 1999. The foregoing applications are herebyincorporated into the present application by reference. Theseapplications depict catheters where the tip region includes multiplehollow fibers. The fibers carry a coolant that is circulated through thecatheter. The thin walls and substantial surface area of the fibers areconductive to the efficient transfer of heat from surrounding bodyfluids/tissue to the coolant, thereby cooling the patient.

Advantageously, cooling catheters are convenient to use, and enabledoctors to accurately control the temperature of a targeted region. Inthis respect, cooling catheters constitute a significant advance. Thisinvention addresses improvements related to such catheters.

SUMMARY OF THE INVENTION

Broadly, the present invention recognizes that wider spatialdistribution of heat exchange fibers in a catheter increases thecatheter's rate of heat exchange. The approach of this invention mayalso be applied in areas other than heat exchange, such as materialsexchange (e.g., the exchange of oxygen or another gas with surroundingblood or other liquid).

To achieve wider fiber distribution, the present invention introducestechniques to selectively shape hollow fibers. Shaping may be performedto introduce divergence (“splay”) among the fibers, or alternatively tointroduce a selected longitudinal oscillation into the fibers. In oneshaping technique, the fibers are held in parallel while opposingassemblies of parallel crimping bars are drawn together on oppositesides of the parallel fibers. When bars of the opposing assemblies drawsufficiently close, they sandwich the fibers in between them, causingeach fiber to assume a shape that oscillates as it repeatedly goes overand then under successive bars. The crimping bars are aligned at obliqueangles to the fibers; thus, the peaks and troughs of each fiber areoffset from every other fiber. While in this position, the fibers areheated and then cooled to permanently establish their shapes. Tofacilitate heating, the bars can be designed to contain a circulatingheating fluid. Or, shape irregularities can be introduced into thefibers during fabrication when the fibers are malleable by directing airor objects against the fibers.

A different shaping technique utilizes a lattice of criss-crossing tinesdefining multiple apertures. In this technique, the lattice and fibersare arranged so that each fiber passes through one of the apertures.Then, the lattice and/or the fibers are slidably repositioned until thelattice holds the fibers with a prescribed outward divergence relativeto each other. While in this position, the fibers are heated and thencooled to permanently retain this shape. In one embodiment, theinvention may be implemented to provide a method to shape a group ofhollow fibers. In a different embodiment, the invention may beimplemented to provide an apparatus such as a group of hollow fibersformed with the foregoing method, or a catheter with such a group offibers.

The invention affords its users with a number of distinct advantages.For example, in comparison with conventional multi-fiber catheters,catheters of this invention exchange heat or materials with improvedefficiency because the fibers are more thoroughly separated from eachother. Either by splaying fibers away from each other, or by creatingfibers that oscillate with a staged phase delay, the inventionencourages fiber spreading. This helps avoid the creation of a commonboundary layer among several fibers, since the fibers are more likely tobe spread apart. The invention also provides a number of otheradvantages and benefits, which should be apparent from the followingdescription of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of an operational sequence for selectively shapinga bundle of hollow fibers to introduce divergence among the fibers, inaccordance with the invention.

FIG. 2 is a perspective view of an exemplary fiber bundle according tothis invention.

FIG. 3 is a plan view of an exemplary one-piece lattice, according tothis invention.

FIG. 4 is a plan view of an exemplary two-piece lattice, including firstand second spacing assemblies, according to this invention.

FIG. 5 is a perspective view of the fiber bundle of FIG. 1 with fibersheld in position by the one-piece lattice of FIG. 3, in accordance withthe invention.

FIG. 6 is a perspective view of a partial fiber bundle to illustratemeasurement of fiber splay, in accordance with the invention.

FIG. 7 is a flowchart of an operational sequence for selectively shapinga bundle of hollow fibers to introduce a selected longitudinaloscillation into the fibers.

FIG. 8 is a perspective view of multiple fibers being held in positionby a retainer, in accordance with the invention.

FIG. 8A is a plan view of an exemplary retainer, in accordance with theinvention.

FIG. 8B is a plan view of a different retainer, in accordance with theinvention.

FIG. 9 is a perspective view of a top crimping assembly being alignedwith fibers, in accordance with the invention.

FIG. 9A is a cross-sectional side view of upper and lower crimpingassemblies with offset base members to permit exaggerated crimping, inaccordance with the invention.

FIG. 10A is a cross-sectional side view of the crimping assemblies beingdrawn together, thereby sandwiching and crimping the intervening fibers,in accordance with the invention.

FIG. 10B is a cross-sectional side view of the crimping assemblies ofFIG. 10A further drawn together to achieve exaggerated crimping, inaccordance with the invention.

FIG. 11 is a plan view of the multiple fibers after undergoing obliquecrimping according to the invention.

FIG. 12 is a perspective cross-sectional view of a crimping bar designedfor containing circulating heating fluid in accordance with theinvention.

FIG. 13 is a schematic view of a fluid circuit for crimping barheating/cooling control.

DETAILED DESCRIPTION

The nature, objectives, and advantages of the invention will become moreapparent to those skilled in the art after considering the followingdetailed description in connection with the accompanying drawings. Asmentioned above, the invention concerns techniques for selectivelyshaping hollow fibers designed to exchange heat or materials with bodyfluids/tissue. As examples, hollow fibers are discussed herein, eventhough the fiber shaping techniques of this invention are similarlyapplicable to solid fibers. These techniques may be applied to introducedivergence among fibers in a bundle as the fibers exit a common point ofattachment, or alternatively to introduce a selected longitudinaloscillation into the fibers.

Fiber Splaying INTRODUCTION

FIG. 1 shows a sequence 100 to illustrate one example of the methodaspect of the present invention. For ease of explanation, but withoutany intended limitation, the example of FIG. 1 is described in thecontext of various hardware components shown in FIGS. 2-6 and describedbelow.

OBTAINING FIBER BUNDLE

The sequence 100, which starts in step 102, describes a process ofshaping fibers to introduce a prescribed divergence as the fibers exitfrom a common source of attachment. In step 104, a fiber bundle isobtained, which includes fibers stemming from a common attachment pointat a distal end of a device such as a catheter 200, shown in FIG. 2. Inthis example, the fibers 202 proceed outward from a fluid transferhousing 204 located at the distal end of a catheter 200. The fibers 202are collectively called a “bundle.” Since they are not bound at theirdistal ends, the fibers are called “free tip.”

When the catheter is assembled, the housing 204 is coupled to asupply/return assembly 206 that includes supply and return conduits forcirculating a fluid to/from the fibers 202. The supply/return assemblymay comprise, for example, parallel or concentric fluid passageways. Thehousing 204 contains paths directing pre-circulation fluid from thesupply conduit to the fibers, and other paths routing post-circulationfluid received from the fibers to the return conduit. In the example ofFIG. 2, each fiber houses separate outward and inward fluid paths.

In one example, the fibers are non-porous and the fluid is a coolantsuch as water, saline, etc., used to cool blood, tissue, or othermaterial that surrounds the catheter 200 while in use. In thisembodiment, the entire catheter, including the fibers, is sealed toprevent any exchange of coolant with the body tissue or fluidsurrounding the catheter. In another example, the catheter 200 containsoxygen, medicine, or another circulating substance that is distributedinto surrounding blood, tissue, or other material surrounding thecatheter 200 through tiny pores (not shown) in the fibers 202.

In contrast to the free tip fibers shown in FIG. 2, the invention may beapplied to other fiber arrangements, such as fibers that are distallyjoined (“bound. tip”), or fibers that individually proceed outward andreturn back to the fluid transfer housing (“looped fibers”) to provide aunidirectional fluid path. Further details of catheters and fiberbundles are explained in the patent applications identified above andincorporated by reference.

OBTAINING LATTICE

In addition to the fiber bundle, step 104 also obtains a fiberpositioning lattice. FIG. 3 shows an exemplary one-piece lattice 300.The lattice 300 is a planar structure that includes horizontal tines 302and vertical tines 304 that criss-cross each other, forming apertures306 between the tines 302, 304. In one example, the tines are spaced byapproximately one millimeter, and comprise a non-abrasive material suchas plastic, stainless steel, etc.

As an alternative to the one-piece lattice 300 of FIG. 3, a multi-partlattice 400 may be used as shown in FIG. 4. The multi-part lattice isespecially useful for bound tip fiber bundles or looped fibers. Thelattice 400 includes first 402 and second 404 spacing assemblies. Thespacing assemblies 402, 404 include respective sets of substantiallyparallel tines 406, 408, thereby forming comb-like shapes. The spacingassemblies 402, 404 may be slid together at right angles until theyoverlap and form a nearly planar structure like the lattice 300. In thisoverlapping configuration, the criss-crossing tines 406, 408 defineapertures (not shown) such as those apertures 306 in the lattice 300.

POSITIONING LATTICE AND FIBER BUNDLE

After step 104, the fibers and desired lattice (300 or 400) arepositioned such that each fiber passes through one of the lattice'sapertures (step 106). In the case of the lattice 300, step 106 involvesindividually routing each fiber's distal end through one of the latticeapertures 306. In the case of the lattice 400, step 106 is performed by(1) sliding the spacing assembly 402 toward the fiber bundle so thatfree ends of the tines 406 pass into the fiber bundle 202 withindividual fibers passing into the spaces between adjacent tines 406,and (2) sliding spacing assembly 404 into the fiber bundle 202 at aright angle to the spacing assembly 406. The assemblies 402, 404 may bebrought together at another angle than perpendicular, however,recognizing that if the angle is too large or small the resultantapertures may be too long to hold the fibers in position.

FIG. 5 shows some fibers 500 after insertion into the lattice 300, aftercompletion of step 106. The fibers 500 only represent some of the fibers202, as the remaining fibers (which would appear in the middle of thelattice) are omitted from this drawing to enhance clarity and reduceclutter.

ADJUSTING DIVERGENCE

After step 106, step 108 is performed to adjust the divergence among thefibers, now routed through the lattice 300. FIG. 6 illustrates fiberdivergence, also called “splay.” Each fiber, such as the fiber 600,exits from the fluid transfer housing 204 at an exit point 604. Withoutany fiber divergence, the fibers would proceed outward from the housing204 in a direction largely parallel to the longitudinal axis of thecatheter 602. Namely, the fiber 600 would proceed outward from its exitpoint 604 along a line 606.

Step 108 adjusts fiber divergence by sliding the positioning latticetoward or away from the housing 204. When the lattice is moved towardthe housing 204, the fiber 600 is bent outward from its normal path 606,increasing its divergence angle 608. Conversely, when the lattice ismoved away from the housing 204, the fiber is not bent outward so much,decreasing its divergence angle 608. Consequently, step 108 involvessliding the lattice along the fibers (or vice versa) until the desireddivergence angles are attained.

HEATING & COOLING

At the conclusion of step 108, the fibers are held in their desiredpositions. To fix this position, the fibers (while held in place by thelattice) are heated to a prescribed temperature (step 110). Thistemperature is sufficiently high to reach a “fixing temperature” atwhich the fibers will retain their current shape even after the fiberscool. This varies according to the materials used. However, in theexample of polyurethane fibers, step 110 may be performed using an ovento heat the fibers to about 180° F. for about one hour.

After step 110, step 112 cools the fibers. This may be achieved at aslower pace by permitting the structure to cool off at room temperature,or more quickly by immersing the fibers and their positioning lattice ina cool water bath. As an alternative to steps 110-112, the fiber shapingsteps 106-108 may be performed during fiber fabrication, when the fibersare malleable.

REMOVING LATTICE

After the fibers cool below their fixing temperature, the lattice isremoved in step 114. Despite removal of the positioning lattice, thefibers retain their shape because of the heat fixing performed in step110. After step 114, the fiber shaping is concluded and the routine 100ends in step 116. Subsequent steps (not shown) are then performed toconstruct and assemble the remainder of the catheter.

Oblique Fiber Crimping INTRODUCTION

FIG. 7 shows a sequence 700 to illustrate another example of the methodaspect of the present invention. For ease of explanation, but withoutany intended limitation, the example of FIG. 7 is described in thecontext of the hardware components of FIGS. 8-11, as described below.The sequence 700, which starts in step 702, describes a process ofshaping fibers to give the fibers a prescribed, periodic waviness. Thefibers are placed side-by-side during shaping. From one fiber to thenext, the peaks and troughs are successively delayed by a prescribedamount as a result of this procedure. Thus, the waveforms defined by thefibers are out of phase with each other. Alternatively, the waveformsmay be irregular (i.e., non-periodic) if desired.

In the context of heat exchange catheters, the fibers comprise hollow,non-porous fibers such as polyurethane. In another example, the cathetermay contain oxygen, a medicine, or another circulating substance that isexchanged with surrounding blood, tissue, or other material surroundingthe catheter through tiny pores (not shown) in the fibers.

In step 704, retaining structures are used to hold the fibers inparallel. Although the fibers may already be mounted to a catheter priorto step 704, this step is more advantageously applied to unattachedfibers, which are more conveniently laid in parallel with each other.

FIG. 8 shows one technique for holding fibers 800 in parallel, usingretainers 802, 804. Each retainer 802, 804 is a two-piece assembly,having respective top members 802 a, 804 a and bottom members 802 b, 804b. Top and bottom retaining members are held firmly together bystructure discussed in greater detail below. In this configuration, thefibers 800 collectively form a ribbon shape having a top side 806 and abottom side 808.

FIGS. 8A-8B further illustrate some exemplary retainers. The retainer820 (FIG. 8A) includes top and bottom members 822, 824 connected at ahinge 823. Opposite the hinge, the members 822, 824 may be clamped,bound, or otherwise fastened together to firmly hold fibers in between.The hinge 823 is merely one embodiment, and ordinarily skilled artisans(having the benefit of this disclosure) will recognize many other meansfor holding the top and bottom members 822, 824 together to sandwich thefibers in between.

The member 822 defines a series of grooves 826 to facilitate moreconvenient, even, and definitive distribution of fibers along the entirelength of the retainer, with each fiber nestling into one groove.Opposite the grooves 826, the member 824 may optionally define a seriesof complementary teeth 828 to firmly hold each fiber in its respectivegroove.

The retainer 830 (FIG. 8B) also includes top and bottom members 832,834. Though shown connected at a hinge 833, fastening of the members832, 834 may be adapted in similar fashion as the retainer 820. Eachmember 832, 834 includes a supple gripping surface 836, 838, such asrubber, foam, or another firm but pliable substance for holding thefibers in place.

In addition to the embodiments 820, 830, ordinarily skilled artisans(having the benefit of this disclosure) will understand that theinvention further contemplates an extensive variety of non-disclosedretainers. One example is a hybrid combination (not shown) of theretainers 820, 830, etc.

As another example (not shown), the proximal retainer may be constructedas shown above, with the distal retainer being a series of parallelposts. This embodiment is useful when each fiber comprises a loop thatproceeds outward and loops back to its point of origination. The distal,looped ends of the fibers are retained by routing the fibers aroundrespective posts of the distal retainer.

PLACING CRIMPING ASSEMBLIES ABOVE/BELOW FIBERS

With the retainers holding the fibers in parallel after step 704, step706 then prepares for crimping of the fibers using crimping assemblies,the structure of which is discussed below. Namely, step 706 places onecrimping assembly above the fibers, and one crimping assembly below thefibers.

FIG. 9 shows an exemplary crimping assembly 902 above the fibers 900(omitting the crimping assembly beneath the fibers 900, for clarity ofillustration). The crimping assembly 902 above the fibers is referred toas an “upper” crimping assembly, whereas the other crimping assembly(not shown) is referred to as the “lower” crimping assembly. These termsare used merely for explanation and clarity of description, however, andterms such as “upper,” “lower,” and the like may be reversed withoutsubstantively changing their meaning.

Each crimping assembly includes a series of substantially parallelcrimping bars, such as the bars 904 of the assembly 902. The size andspacing of the bars is selected depending upon factors such as the fiberdiameter, fiber material, desired crimping pattern, etc. Although otherarrangements may be used, the bars of the upper crimping assembly may besubstantially equidistant, as with the bars of the lower crimpingassembly. Furthermore, the distance between bars in the upper crimpingassembly may be the same (or different) than the distance between barsin the lower crimping assembly, depending on the desired shape ofpost-crimping fibers.

The distance between adjacent crimping bars (measured center-to-center)defines the span between adjacent peaks and troughs in a fiber, i.e.,one-half of the fiber's wavelength. The space between adjacent crimpingbars is necessarily greater than the fiber diameter, to permit thefibers to run between the bars.

As an example, the crimping bars 904 may be mounted in position by abase member (not shown) secured to one end of each bar 904. Oneadvantage of this single-base-member arrangement is that the crimpingassemblies may be interleaved by positioning their base members towardthe outside, with the bars' open ends coming together. Alternatively,two base members may be used for each crimping assembly, where one basemember spans one end of the bars 904, and another base member spans theopposite end of the bars 904.

FIG. 9A provides a cross-sectional depiction of a different example,which permits the bars of the two crimping assemblies to be broughttogether and actually past each other to cause a more drastic crimp. Inthis example, the bars of each crimping assembly are held in position bya base member that is offset from the axes of the bars. Moreparticularly, the crimping assembly 950 includes bars 956 mounted to anoffset base member 951; similarly, a crimping assembly 952 includes bars957 mounted to an offset base member 953. With this arrangement, thebars 956, 957 may be brought into alignment with each other by urgingthe base members 951, 953 together; moreover, by continuing this motionone set of bars may actually be driven past the other set of bars toprovide an exaggerated crimping configuration.

ALIGNING CRIMPING ASSEMBLIES

After step 706, the upper and lower crimping assemblies are aligned sothat bars of the upper and lower assembly are substantially parallel toeach other, and so that the parallel bars form an oblique angle to theparallel fibers. After crimping, the place where each bar contacts afiber will provide a peak or trough in an oscillating pattern along thelength of the fiber. Namely, the bars of one crimping assembly willdefine all fiber peaks, with the bars of the other crimping assemblydefining all troughs (or vice versa). Step 708 reduces the likelihoodthat any two fibers reach their peaks and troughs at the same positionalong their lengths. This is the reason for the oblique alignment ofbars with the fibers. To illustrate this in more detail, the bars arepositioned so that the angle 980 (FIG. 9) formed with the fibers isneither 0°, 90°, 180°, nor 270°. In other words, the angles that thebars form with respect to the fibers are oblique, i.e., neither parallelnor perpendicular.

Equation 1 shows an exemplary computation of the angle 980.angle 980=tan⁻¹ (x·n)   [1]where:

-   -   x=the distance between adjacent fibers.    -   n=the number of fibers.    -   =the desired fiber wavelength, i.e., distance between successive        peaks or troughs in one fiber.

Equation 1 computes the angle 980 such that, during the span of onefiber wavelength, all fibers successively reach their peak height, withnone repeating. Ordinarily skilled artisans (having the benefit of thisdisclosure) will recognize a variety of other techniques for computingthe angle 980, further description being unnecessary to the presentdisclosure.

DRAWING CRIMPING ASSEMBLIES TOGETHER

After the alignment of step 708, step 710 draws the upper and lowercrimping assemblies together. The relative distance between the upperand lower crimping assemblies is reduced until the fibers bend intooscillating shapes that repeatedly curve back and forth longitudinallyalong the fibers, as the fibers pass around bars of the upper and lowerassemblies in alternating fashion. FIG. 10A shows one example, where afiber 1000 is being crimped between bars 1002 of an upper crimpingassembly and bars 1004 of a lower crimping assembly. If desired, thecrimping assemblies may be drawn past each other to achieve exaggeratedcrimping as shown in FIG. 10B.

If desired, step 710 may adjust tension on the fibers by changing thedistance between the retainers (e.g., 802, 804 of FIG. 8) that hold theopposite ends of the fibers. Decreasing this distance releases strain onthe fibers as the crimping assemblies re-route the fibers into a paththat is longer then the straight distance between the fibers' ends dueto the paths' repeated curves. Otherwise, without any narrowing of theretainers, the fibers may be excessively stretched or sheared while thecrimping assemblies force the fibers to assume a longer, curving path.During step 710, the tension across the fibers may be selectivelyadjusted to form tighter crimps and a more triangular fiber oscillation(using more tension), or alternatively looser crimps with a moresinusoidal oscillation (using less tension).

HEATING & COOLING

With the crimping assemblies sandwiching and effectively crimping thefibers as discussed in step 710, this configuration is held while thefibers are heated (step 712). The fibers are heated to a fixingtemperature, causing the fibers to permanently maintain their crimpedshape, despite subsequent cooling. This temperature varies according tothe materials used. In the example of polyurethane fibers, step 712 mayinvolve placing the fibers, retainers, and crimping assemblies into anoven and heating at 180°0 Fahrenheit for about one hour. To facilitateheating and/or cooling of the fibers, crimping bars 910, similar to bars904, 956 and 957, may be provided with circulating fluids therein. Thebars 910 in such an arrangement would comprise a hollow structure havingthin, heat conducting walls and defining one or more lumens throughwhich a heat exchange fluid can be circulated. FIG. 12 illustrates sucha structure, in which crimping bar 910 comprises a tube 912 havinglumens 914 and 916 formed therein. It will be appreciated that otherlumen arrangements can be provided, for example using concentricstructures. Arrows A and B indicate the directions of fluid circulationin lumens 914 and 916, respectively. The circulated heat exchange fluidcan be water or other liquid, or it can be a suitable gas. FIG. 13 showsan exemplary fluid circuit, in which a heat exchange module 920 is shownto include a fluid reservoir 922 in fluid communication with bar 910, aheating component 924 for heating the circulating fluid, a coolingcomponent 926 for cooling said fluid, and a control unit 928 forproviding precise control of the applied heating/cooling cycle(s) inaccordance with a designated regimen which is for example preprogrammedinto an electronic processor 940 through an input device such as akeyboard 942. To improve temperature control, processor 940 can receivefluid temperature measurements from a measuring device 944 which sensesfluid temperature either at reservoir 922 or at a different location inthe fluid circuit to thereby provide temperature feedback control.

After step 712, while still holding the fibers in their crimpedposition, the fibers are cooled (step 714). The fibers may be cooled byvarious techniques, such as removing them from the oven and letting themcool to room temperature, immersing the fibers in water or anothercooling liquid, etc. During cooling, the fibers are still held incrimped form by the retainers and crimping assemblies to ensure thatthey cool beneath the fixing temperature while held in the desiredposition.

REMOVING CRIMPING ASSEMBLIES

After cooling, step 716 removes the crimping assemblies and retainers.Due to the heat shaping previously described, the fibers retain theircrimped shape despite removal of the crimping assemblies. As a practicalmatter, the crimping assemblies may be removed earlier if desired, aslong as the fibers have cooled sufficiently that they are no longeramenable to heat shaping.

After completing the sequence 700, fibers remain crimped as shown byFIG. 11. Namely, each of the fibers 1100 oscillates sinusoidally alongits length, presenting a series of troughs (such as 1104) and peaks(such as 1102). No two fibers reach a peak or trough at the same point.Instead, the fibers 1100 reach their peaks and troughs in successiveorder from the top of the page down, as viewed in FIG. 11. The fibers'peaks are aligned along lines such as the line 1106, the line 1108, etc.

OTHER EMBODIMENTS

While the foregoing disclosure shows a number of illustrativeembodiments of the invention, it will be apparent to those skilled inthe art that various changes and modifications can be made hereinwithout departing from the scope of the invention as defined by theappended claims. For example, the present crimping fixture can beestablished by plural grooves, each describing a predetermined waveformdifferent from the outer grooves, with fibers having mandrels insidebeing laid in the grooves and then heat treated as aggregate to causethe fibers to permanently assume the shapes of the respective grooves.Furthermore, although elements of the invention may be described orclaimed in the singular, the plural is contemplated unless limitation tothe singular is explicitly stated.

1. A method for shaping a group of multiple fibers, comprising theoperations of: holding the fibers substantially parallel to each otherto form a plane defining top and bottom surfaces; positioning an uppercrimping assembly of substantially parallel crimping bars proximate thetop surface; positioning a lower crimping assembly of substantiallyparallel crimping bars proximate the bottom surface; aligning the upperand lower crimping assemblies such that the bars are substantiallyparallel to each other, and the bars form an oblique angle to thefibers; decreasing relative distance between the upper and lowercrimping assemblies sufficient to bend the fibers into oscillatingshapes that repeatedly curve back and forth longitudinally along thefibers as the fibers pass around bars of the upper and lower crimpingassemblies in alternating fashion; and before or while the fibers arebent into the oscillating shapes, heating and/or cooling the fiberssufficiently for the fibers to adopt the oscillating shapes when cooled,at least one said heating and/or cooling comprising circulating a heatexchange fluid through one or more crimping bars of at least one of saidupper and lower crimping assemblies.
 2. The method of claim 1, adjacentbars in the upper crimping assembly being substantially equidistant. 3.The method of claim 1, adjacent bars in the upper crimping assemblybeing separated by a first distance, and adjacent bars in the lowercrimping assembly being separated by the first distance.
 4. The methodof claim 1, the holding operation releasing sufficient longitudinaltension on each fiber to permit bending of the fibers into substantiallysinusoidal shapes.
 5. The method of claim 1, wherein the heating andcooling are effected automatically in accordance with preprogrammedregimen.
 6. The method of claim 1, wherein the heating and coolingincludes temperature feedback control.
 7. The method of claim 1, theoperation of decreasing relative distance moving at least one of thecrimping assemblies such that the crimping assemblies proceed past eachother.
 8. The method of claim 7, the holding operation maintainingsufficient longitudinal tension on each fiber such that movement of thecrimping assemblies past each other bends the fibers into oscillatingtriangular shapes.